Plasma Wave Radiation Induced by a Conducting Tethered Satellite System

During the planned electrodynamic tethered satellite system (TSS-1) experiment, a large, conducting subsatellite will be tethered to the space shuttle. The long, surface -insulated tether wire will electrically couple the two satellites, thereby forming a large conductor which moves in a magnetized plasma. One of the scientific objectives of the experiment will be the excitation of plasma waves. This thesis considers the processes of wave excitation through theoretical models and constructs estimates of the total radiated power and frequency spectrum. It is shown that wave excitation arises not directly from the current flow within the tethered system but rather the collection of this current from the plasma at the two uninsulated ends. The wave radiation is thus found to be critically dependent on the current distribution at the tethered system's end-connectors. A new current system is therefore developed which models current collection by a large, spherical satellite. It is shown that the model current system radiates in two discrete frequency bands. Band I (0 < omega < Omega_{rm i}) has been proposed in several previous studies, beginning with Drell et al. (1965). The new results for this band are consistent with earlier studies. Of special interest is the higher frequency band II (omega_{rm 1hr} < omega < Omega _{rm e}), the power in which is found to be 1-2 orders of magnitude greater than in band I. The importance of band II was first noted by Barnett and Olbert (1986). A new model is constructed here which shows the relationship between the various wavelengths in the plasma and the moving current source. In particular, it is shown that the low frequency waves form a large, co-moving structure in which oppositely charged wave surfaces in the plasma are matched to the two ends of the tethered system. At these frequencies the system is a single, large, coherent radiation source. In the high frequency band, however, the waves are produced locally by the motion and charge interaction of the satellite's conducting surface. Here, the two ends of the system are completely independent, localized, radiation sources. The conclusion of the theoretical model is that the total radiated power is maximized by (1) reducing the diameter of the satellite, (2) eliminating plasma sheath formation, and (3) drawing the highest possible current to the satellite's outer surface.